1. Field of the Invention
The present invention relates to a broadband source of picosecond radiation and, more particularly, to a tunable broadband source of picosecond radiation formed with only a picosecond pulse source and a liquid core single mode optical fiber.
2. Description of the Prior Art
Tunable picosecond sources in the visible and near infrared spectral regions are needed for optical fiber diagnostics, device characterization, and the study of semiconductor physics. Also, the generation of infrared picosecond pulses has received increasing attention over the last several years, principally for optical communications, the investigation of multiple-photon absorption and vibrational energy transfer processes in molecules, and for laser fusion. Picosecond pulses have been generated in the infrared region (1.3-3.6 micrometers) in the past using 1.06 .mu.m optically pumped lithium niobate optical parametric devices in the traveling wave mode, as disclosed in the article "Intense Tunable Picosecond Pulses in the Infrared" by Laubereau et al appearing in Applied Physics Letters, Vol. 25, No. 1, July 1974 at pp. 87 et seq.
A recent arrangement for generating picosecond pulses is disclosed in U.S. Pat. No. 4,349,907 issued to A. J. Campillo et al. on Sept. 14, 1982. As disclosed, intense 1.064 .mu.m picosecond pulses pass through a 4.5 cm long LiNbO.sub.3 optical parametric oscillator crystal set at its degeneracy angle. A broadband picosecond output pulse emerges, and a simple grating and mirror arrangement is used to inject a selected narrow-band pulse into a 2 cm long LiNbO.sub.3 optical parametric amplifier crystal along a second pump line. Typical input energies at 1.064 .mu.m along both pump lines are 6-8 mJ for the oscillator and 10 mJ for the amplifier. This yields 1 mJ of tunable output in the range 1.98 to 2.38 .mu.m which when down-converted in a 1 cm long CdSe crystal mixer gives 2 .mu.j of tunable radiation over the 14.8 to 18.5 .mu.m region. The bandwidth and wavelength of both the 2 and 16 .mu.m radiation output are controlled solely by the diffraction grating. Although the above-described arrangement is capable of generating tunable picosecond pulses, the arrangement is complicated, expensive, and too involved to become useful outside the laboratory environment.
Yet another arrangement for generating such pulses is discussed in the article "Tunable Subpicosecond Pulse Generation for 535 to 590-nm by a Hybridly Mode-Locked Dye Laser", by Y. Ishida et al appearing in the Japanese Journal of Applied Physics, Vol. 21, No. 5, May, 1982 at pp. L312-L314. Here, tunable subpicosecond pulses are stable generated in the above-cited wavelength range for a cw mode-locked dye laser system using rhodamine 110 and disodium fluorescein active dyes, employing combined passive and synchronous mode-locking. A minimum pulse width as short as 0.25 ps has been achieved with this arrangement at approximately 560 nm. As disclosed, however, this arrangement appears to comprise a limited range of tunability.
The problem remaining in the prior art, therefore, is to provide a means for generating picosecond and subpicosecond pulses which provides a wide range of tunability without requiring an inordinately complicated arrangement.